Photoplethysmography (PPG) and pulse oximetry (PO) measurement systems may use a light emitting diode (LED) to illuminate the skin of a subject and a photodetector to capture reflected light from the subject in order to determine heart rate and oxygen saturation of the blood. Conventional approaches may drive the transmitting LED at maximum power, while relying on a central processing unit (CPU) to adjust the gain of programmable amplifiers that amplify analog signals from the photodetector (e.g., to take the programmable amplifiers out of saturation). Such an approach may increase delays and power consumption. For example, the receive path to the CPU may be relatively complex and may include an analog to digital conversion (ADC) stage that introduces considerable delay. Additionally, components such as the CPU, ADC, main crystal oscillator, etc., may consume substantial power.